This invention relates to metal-cleaning compositions. More particularly, this invention relates to an aqueous metal-cleaning composition and method of using same, wherein the composition is capable of substantially removing industrial-type soil contaminants from metal surfaces at low wash temperatures without the help of any mechanical action.
Many industries, such as, for example, automobile parts repair and replacement services and the like, require that component mechanical parts be cleaned prior to inspection, repair, or replacement thereof. Generally, such parts have been exposed to various industrial-type soil contaminants such as dirt, grease, oil, ink and the like, which must be removed for effective repair or service.
A variety of metal cleaners have been used to clean such mechanical parts. For example, solvent-based metal cleaners have been used which contain either halogenated or non-halogenated hydrocarbons. Aqueous-based, highly alkaline detergent systems have also been used to clean metal parts. However, the use of such solvent-based or aqueous-based cleaners has raised environmental and/or worker safety concerns.
For example, although halogenated hydrocarbon solvents such as chlorofluorocarbons (CFCs), trichloromethane, methylene chloride and trichloroethane (methyl chloroform) have been widely used in industry for metal cleaning, the safety, environmental and cost factors associated with their use coupled with waste disposal problems are negative aspects of the use of such solvents. A world-wide and U.S. ban on most halogenated solvents is soon in the offing by virtue of the Montreal Protocol, Clean Air Act and Executive and Departmental directives.
Non-halogenated hydrocarbon solvents such as toluene, Stoddard solvent and like organic compounds such as ketones and alcohols are generally flammable and highly volatile and have dubious ability to be recycled for continuous use. These factors, along with unfavorable safety, environmental and cost factors, make the non-halogenated hydrocarbon solvents unattractive for practical consideration. For example, the most useful organic solvents, classified as volatile organic compounds (VOCs), pollute the atmosphere, promote formation of a toxic zone at ground level, and add to the inventory of greenhouse gases.
Aqueous cleaning systems have been developed to overcome some of the inherent negative environmental and health aspects associated with the solvent-based cleaning systems. Unfortunately, aqueous cleaning systems also have drawbacks.
For example, aqueous solutions used to clean industrial-type soil contaminants from metal surfaces are generally effective only at relatively high wash temperatures, e.g., 140.degree. F. and above. Such high wash temperatures are disadvantageous because of the higher energy costs which are involved relative to lower temperature washing and the difficulty with maintaining such high temperatures. Unfortunately, with aqueous solutions, a reduced wash temperature usually leads to reduced cleaning versus that obtained at higher wash temperatures. It would be desirable, therefore, to provide an aqueous metal-cleaning composition which provides high cleaning performance at relatively low wash temperatures.
Another advantage associated with the use of aqueous cleaners stems from the high surface tension of water and the propensity of the detersive agents in the aqueous cleaner to foam upon agitation of the cleaning bath such as induced in the bath or by the use of spray nozzles to apply the cleaning solution to the metal components being cleaned. The foaming profile of an aqueous cleaner is an important characteristic. The presence of foam often renders the use of machines with high mechanical agitation impractical due to excessive foaming. High foaming cleaners are particularly problematic in spray equipment. In addition to foam exiting the equipment, foaming can cause pump cavitation and selective loss of surfactants. Also, the presence of foam can cause the overflow of liquids onto floors as well as cause difficulties with viewing the cleaning process through vision ports and the like contained in the machinery. Contrary to popular belief, foaming does not contribute to cleaning and, therefore, is not necessary for immersion or spray cleaning. Generally, low foaming cleaners are preferred because they can be used in dip, immersion, ultrasonic and spray equipment.
It has been found that, in conventional aqueous metal-cleaning compositions, foam formation will decrease with increased temperature. Thus, with such compositions, the use of relatively low wash temperatures tends to lead to high foam formation, which renders such cleaning compositions unsuitable for use at low temperatures.
As stated above, agitation of the cleaning solution appears to induce foaming. Thus, one way to reduce foam formation would be to reduce or eliminate the agitation of the cleaning solution. It would be desirable, therefore, to provide an aqueous metal-cleaning composition which is capable of substantially removing industrial-type soil contaminants from metal surfaces at low wash temperatures without substantial agitation of the cleaning composition, thereby avoiding excessive foaming during use of the composition.
A further drawback associated with aqueous cleaners containing sodium hydroxide or organic solvents such as alkanolamine, ethers, alcohols, glycols and the like, is that such cleaners tend to be exceedingly alkaline, i.e., having pHs of 13 and above. These exceedingly alkaline aqueous solutions are highly corrosive to metal surfaces, highly toxic and can be dangerous to handle, thus requiring extreme safety measures to avoid contact with the skin. Organic solvent-containing aqueous cleaners have the toxicity and environmental problems discussed previously herein.
Thus, it is also desirable to provide a low-temperature aqueous cleaning composition which is not highly corrosive to metal surfaces, toxic or dangerous to handle.
It is also important that the aqueous metal cleaners be reusable to render such cleaners economically viable. Thus, it is not practical on an industrial scale to sewer an aqueous cleaning bath upon a single usage thereof. Many of the aqueous-based cleaners now available use detersive agents which are effective in removing the dirt, grease or oil from the metal surface but which unfortunately readily emulsify the contaminants such that the contaminants are highly dispersed or solubilized throughout the aqueous solution. These highly emulsified cleaning solutions are difficult to treat to separate the contaminants from the aqueous cleaner and, accordingly, the cleaning solution gets spent in a relatively short period of time and must be replaced to again achieve effective cleaning of the metal parts and the like. It would be desirable to provide an aqueous metal cleaner which could effectively remove the contaminants from the metal surface but which would allow the ready separation of such contaminants from the cleaning solution to allow effective and prolonged reuse of the solution.
In addition to the above-recited desirable characteristics, it is also desirable that an aqueous metal cleaner be compatible with a relatively wide variety of metals so that such cleaner can be used to clean a wide variety of metal substrates.
Accordingly, a primary object of this invention is to provide an aqueous metal-cleaning composition capable of effectively removing industrial-type soil contaminants from metal surfaces at relatively low wash temperatures.
A further object of this invention is to provide an aqueous cleaning composition which is capable of effectively removing industrial-type soil contaminants from metal surfaces at relatively low wash temperatures and in the absence of substantial agitation of the aqueous cleaning composition, thereby avoiding substantial foaming of the composition during use thereof.
A still further object of this invention is to provide a low-temperature, aqueous metal-cleaning composition which effectively removes industrial-type soil contaminants from a metal surface but which also allows ready separation of the soil contaminants from the aqueous composition so as to permit effective and prolonged use of the cleaning composition.
Another object of this invention is to provide a low-temperature, aqueous metal-cleaning composition which is not highly corrosive to metals, toxic or dangerous to handle.
A further object of this invention is to provide a low-temperature, aqueous metal-cleaning composition which is compatible with a relatively wide variety of metals.
Still another object of this invention is to provide a method of removing industrial-type soil contaminants from metal surfaces at low temperatures by means of an alkaline aqueous cleaning composition having the properties described in the foregoing objects.
These and other objects which are achieved according to the present invention can be readily discerned from the following description.